This is a great resource for answers, help, & advice to aquarium and pond questions not found elsewhere; With regular posts & article updates. In our research; we use aquaculture, horticulture, medical, & university research to compile many of our articles.

The most common symptom these bacteria will show as cloudy eyes and although majority of most aquarium bacterial infestations are gram negative, most eye infections are generally gram positive and caused by Streptococcus or related bacterium

Occasionally Aeromonas in freshwater or Vibrio in saltwater will show up as eye infections, especially in “Pop Eye”.
In this case, following treatment for Aeromonas and Vibrio are is recommended as these are gram negative anaerobic & aerobic bacteria.

Although “Cloudy Eyes” (corneal opacity-whitish eyes) is the most common symptom of these gram positive infections, other symptoms are possible such as:

"Pop-eye" (though usually caused by Aeromonas),

Hemorrhages in or around the eye

A “milky” slime

Erratic swimming

Swim bladder issues (inability to regulate buoyancy) & lethargy

Darkening of body (such as a “black moldy appearance

Occasionally Streptococcus can appear as a mouth 'fungus', on the gill plate, base of the fins, vent/anus, or elsewhere on the body although usually this is a symptom of Columnaris or Saprolegnia.
Reference: Columnaris & Saprolegnia

On rare occasions Streptococcus may be a cause of Dropsy.
As well some cases of “False Neon Tetra Disease” (FNT) may also be caused by Streptococcus.

Often fish with Streptococcus iniae infections will not eat, which can complicate treatment for this bacterium when it is internal, especially for freshwater fish which do not drink water they are contained in (unlike most marine fish).
Further Reading: Do Fish Drink?

Most bacterial diseases of fish are opportunistic (such as Aeromonas or Columnaris). Streptococcus on the other hand, does not seem to be a truly opportunistic pathogen, as it can be more aggressive than many other environmental bacteria.

In one experimental study (Ferguson et al. 1994), populations of zebra danios and white clouds exposed to high concentrations of Streptococcus in the water experienced 100% mortality within 2-4 days of exposure.
For this reason it is important that Streptococcus infections be quickly identified and managed to prevent major losses.

It is also noteworthy that recent studies have also shown growing incidents of this bacterial infection in fish farming, which is where most of the research into Streptococcus in fish is made available from.
In fact this problem has become severe enough among Tilapia and Trout farms that a vaccine is now in the testing phase for Streptococcus iniae.
Reference: First Live-Attenuated Vaccine for S. Iniae in Development

Fish that have been documented most susceptible include rainbow sharks, red-tailed black sharks, rosy barbs, danios, and some tetras and some cichlids.

TREATMENT

For most “full blown” Streptococcus infections (not necessarily a mild eye infection), Erythromycin is often the drug of choice.
Mortality should cease within 48 hr of treatment with the correct antibiotic if complicating factors are not present.

If the disease is internal, this therapy may be difficult because erythromycin does not absorb well, and this case treatment with Neomycin enhanced foods foods is recommended.
Further Reading: Aquarium Medications; Fish Food Delivery

It should be noted that although Erythromycin is the drug of choice, because it is an effective anti gram positive bacterium medication, it is also very hard on nitrifying bacteria, so having cultured sponge filters or other “seasoned” filter media to replace during and/or after treatment is very important since Streptococcus is not opportunistic. Many opportunistic bacterium such as Columnaris may follow, especially if ammonia/nitrites rise during or after treatment.
Further Reference: Aquarium Nitrogen Cycle; Use of Medications

Although generally the antibiotic of choice, sometimes Streptococcus bacterium can build a resistance to Erythromycin (as well sometimes destruction of tank environment from the use of Erythromycin can be a double edged sword that renders this antibiotic ineffective especially if tank conditions are not closely monitored).
In this case, Doxycyline or Tetracycline Hydrochloride may be a good substitute with Doxycyline more often being the better choice.

Tetracycline is not without its side effects either and its use can severely lower red blood cell counts in fish, so increasing circulation is a must.
As well, it's hard on nitrifying bacteria and tends to cause a buildup of brown foam. Tetracycline or Doxycyline should never be combined with Erythromycin.

Kanamycin combined with Nitrofurazone (Furan 2) (Nitrofurazone is especially useful for topical infections that may show as a milky slime) or Neomycin (in food for suspected internal infections).
Product Source: Kanacyn (Kanamycin) from AAP

Minocycline in the same combinations in place of Kanacyn.
The advantage of possibly using Kanacyn is that this medication (combined with Nitrofurazone) can also prevent/treat opportunistic Columnaris or Aeromonas infections that may arise.

Melafix is a reasonable preventative treatment and may be effective for mild Streptococcus infections.
Sometimes for very mild eye infections (no other symptoms) Melafix is the only "in-tank" treatment you may need to use (outside of direct application of treatment).
Further Reading: Aquarium Medications Part 4; Organic Treatments

If eyes are directly affected (and the only primary target of this infection), removing the fish and treating the fish directly in the eyes with Silver Nitrate followed by Potassium Dichromate is extremely effective.
The only problem being that Silver Nitrate is hard to find, although sometimes photo lab supply businesses may have it.Pictured to the right is Eye Fungex by Aquatronics containing Silver and Potassium Dichromate, but unfortunately this a difficult product to currently obtain.

Another choice is Merbromin, which too can be swabbed, painted, or dropped directly on the eyes. While not as effective as the Silver Nitrate/Potassium Dichromate combination, it is also easier to use.

Potassium Permanganate is reasonable third choice for this direct eye application and Methylene Blue a third choice for direct application.
Either way, sometimes the only “in tank treatment” that may have to followed up with when the eyes are treated directly is Melafix (used in the main tank or hospital tank, not in a bath).

Medicated Baths may also be a very useful part of treatment for external Streptococcus infections in fish.
These would be twice daily for 30 minutes and I recommend the use of Methylene Blue combined with a double dose of Erythromycin or Tetracycline, or even Usnea

If you suspect that you have a group of fish with a Streptococcus infection, the affected population should be isolated from all others. If possible, have dedicated equipment (nets, siphon hoses) for these fish.

Use of anti-septic treatments such as Melafix, especially after injury or similar is helpful for prevention or even treatment early in Streptococcus infections.
Think of it this way, many human infections (including Staph) are common and simple treatments with products such as Neosporin is all that is necessary in minor injuries to prevent a major infection.
Although Melafix has little or NO anti gram negative bacterial abilities, it is an excellent preventive even for diseases such as Columnaris from getting a “foothold” by killing off disease pathogens such as Streptococcus that may be followed by Columnaris.

Are you looking for an informative and friendly Aquarium Forum to help with your fish problems (or simply to share your experience)?
Consider this forum with a friendly family atmosphere:Everything Aquatic Aquarium Forum

Premium, second to NONE Aquarium Bio Filters, that with optional Oolitic Sand, also maintains essential aquarium calcium levels, alkalinity, & electrolytes that are important to ALL Marine life, Goldfish, African Cichlids, Livebearers & more

Fish NutritionComplete information from fish food building blocks to sources and much more

AquaMaster ULTRA PREMIUM Mini Tropical Fish FoodDual-color slow-sinking crumbles specially designed for small tropical fish to enhance paltability and feeding rate.
Includes Probiotics added to help digestion and to reduce nitrates & water pollution.

Remember, it is your purchases (both small & large) at our primary sponsor, AAP, that keeps these world class information articles free.Or please consider a donation (especially International users of this information), even just $5 usd helps.
As our primary sponsor is AAP, which provides little income for its owner after paying staff (including to help others) & upkeep of this information!

If only 10% of users of this information donated $5, this information will be able to remain free in the future!

AQUARIUM ANSWERS;
ARTICLES:In Chronological order of writing with the newest at the top

If you have found this site helpful (or the sister site Aquarium and Pond Information),
please consider adding a link to one of our articles from your own blog or website.

American Aquarium Products along with "Aquarium/Pond Answers", and our VAST library of aquarium & pond keeping information found NOWHERE else in the word is currently FOR SALE for the right offer from an entity that will carry forward this company's 35+ year legacy of unique information (this also includes several other web and blog sites as well).
Only serious inquiries from qualified potential buyers will be considered

Recommended Related Information Sites & Products from our family of PROFESSIONAL aquarium and pond websites:

All articles are the copyrighted material of Carl Strohmeyer, these can be used ONLY in part and only with proper hyper link.
Use with Google Adwords/Adsense is STRICTLY prohibited without revenue sharing